1. Field of the Invention
The present invention relates to a detergent composition containing a specific aminodicarboxylic acid-N,N-dialkanoic acid or its salt, and a synthetic surface active agent. More particularly, it relates to a detergent composition which does not form metallic soap in washing water with high hardness, and gives little corrosive effect to the surface of such light metal materials, e.g., aluminum and others, and exhibits high solubility even in water with low temperature, leading to an excellent washing performance, and, moreover, is excellent in biodegradability (microbial degradability), and, furthermore, is particularly suitable for washing clothes and the hard surface of various facilities and apparatuses made of light metal materials.
2. Background of the Invention
In recent years, environmental keeping has strongly been advocated, and microbial degradability of both synthetic surface active agents and builders which are used for washing, and also eutrophication by phosphorus compounds has been taken up as social problems. Therefore, there is a tendency recently that cleaning agents for clothes change from synthetic detergents to soap compositions.
Soap compositions have excellent microbial degradability. But though they show excellent washing effect if they are put in water with good quality and relatively high temperature, they are likely to get influenced by the hardness or the temperature of washing water. Namely, if water with high hardness or low temperature is used, metallic soap insoluble to water is formed, or soap compositions themselves become hard to dissolve in water and change to insoluble materials, resulting in decrease in washing effect. Those insoluble materials are deposited on fiber surface, e.g., when at washing fabrics, and thus deposited materials are not removed even if rinsed with water, resulting in deterioration of the finish after washing. This is the reason why the transfer from synthetic detergents to soap compositions is retarded.
As a means of solving the problem involved in the above-described soap compositions, blending soap compositions with the chelating agent, such as an alkali salt of ethylenediamine tetraacetic acid (EDTA) and alumina silicate (zeolite) has conventionally been used. However, the said EDTA chelating agent is poor in microbial degradability and, as a result, a soap composition containing EDTA becomes also poor in microbial degradability. Moreover, the zeolite chelating agent has weak sequestration and, as a result, water-insoluble metallic soap is formed when a soap composition containing zeolite is used in water with high hardness. Furthermore, even if those chelating agents are contained in soap compositions, this fact does not improve solubility of the soap composition in water with low temperature, and thus the problem of water-insolubility remains unsolved.
Recently, as the interest in protection of limited resources has increased, development and utilization of resources which can be reclaimed or recovered has become a new subject. In particular, regarding kitchen detergents, a change of an anionic surface active agent over to a biodegradable nonionic surface active agent has been progressing. Since the raw material source of this nonionic surface active agent is plant, it has excellent microbial degradability and is mild to skin, namely, less irritant to skin and, in addition, has excellent degreasing property. Therefore, the nonionic surface active agent is suitable for synthetic detergents for kitchen use, mainly for washing tablewares. However, when the nonionic surface active agent is used alone, washing effect is low as a synthetic detergent for fabrics. Therefore, for the purpose of raising the washing effect of this surface active agent, a mixture of a surface active agent and a builder compound has been used. Though phosphorus compounds have conventionally been used as the builder compound of this kind, the use of such compounds is a cause of unpreferable eutrophication and, therefore, a chelating agent showing calcium sequestration, such as alumina silicate (zeolite), high molecular carboxylate with polyacrylate being a representative example, nitrilotriacetate (NTA) and ethylenediamine tetraacetate (EDTA) have been used instead in recent years.
However, the alumina silicate is weak in sequestration and, as a result, a detergent using the alumina silicate greatly decreases its washing effect when used in water with high hardness. Moreover, the alumina silicate is water-insoluble. Therefore, when a detergent containing the alumina silicate is drained off, the alumina silicate is deposited in a sludge state on the bottoms of sewage treatment plants or the beds of rivers and others, which will cause a new environmental problem. The above-described high molecular carboxylate and ethylenediamine tetraacetate as a chelating agent has poor microbial degradability and, as a result, a synthetic detergent containing those chelating agents, such as high molecular carboxylate, is also poor in microbial degradability. Regarding nitrilotriacetate, though its microbial degradability is excellent and its environmental problem has been solved, it is regarded as a builder hard to employ, from the standpoints of safety and washing performance. Moreover, most of surface active agents which have conventionally been used as the main component of the above-described known detergents use hydrocarbons derived from petroleum as raw material sources which can not be reclaimed or recovered. Therefore, if the importance of resource protection in future is taken into consideration, those surface active agents involve a big problem.
Furthermore, various light metal materials including aluminum material have recently been used in packing apparatus of drinks and food processing facilities which requires precision, or in vehicles, aircrafts, containers, and the like which all require light weight. But it is necessary to wash the outer surface, i.e., hard surface, of apparatuses, facilities, vehicles, aircrafts, containers and the like which use light metal materials with a detergent having high washing effect.
Detergents containing chelating agents, such as sodium ethylenediamine tetraacetate (EDTA), and having a high pH value, have conventionally been used as detergents having high washing effect.
However, if such detergent as having a high washing effect contacts the surface of a light metal material for a long period of time by repeated washing, there may occur such problems that the surface of the light metal material gets corroded. Or whitening or blacking phenomena occurs, resulting in disappearance of surface luster, or the detergent dissolves the surface and makes holes on it.
In addition, in order to efficiently wash a wide area of hard surface, foam cleaning technique was recently employed. In this technique, an anionic surface active agent is incorporated in a detergent for the purpose of increasing foaming.
However, the anionic surface active agent is greatly influenced by hardness of water used in dilution and, if it is diluted with water having high hardness, the anionic surface active agent becomes insoluble and foaming does not occur and, at the same time, washing performance drops.
In order to solve those problems, a chelating agent, such as sodium ethylenediamine tetraacetate (EDTA), is incorporated in the detergent which contains an anionic surface active agent in the same manner as described above. However, the detergent containing a chelating agent, such as EDTA, causes the above problems at light metal materials.
Thus, in washing light metal materials, such as aluminum, if it is aimed to increase washing effect of the detergent by adding a chelating agent, the same problem as mentioned above occurs on the surface of light metal materials.
Therefore, as a detergent for washing the surface of light metal materials, a detergent containing selected nonionic surface active agent which has lower foaming property but gets less influenced by the hardness of diluting water and having pH value being adjusted as close to neutral, or a detergent added with a silicate which is effective to prevent light metals from corrosion, and unnecessary to contain a chelating agent such as EDTA, is required.
However, the detergent of this type has low washing performance. Therefore, at washing, it is necessary for the detergent to contact the surface of light metal material for a long period of time, or to employ physical means, such as rubbing the surface. Further, since the foaming property is low, the said detergent is not suitable for foam washing which is good at washing the large area. When an anionic surface active agent is used, a detergent which does not contain a chelating agent, such as EDTA, is influenced by the hardness of diluting water and becomes difficult to get foams. Therefore, a large amount of a surface active agent is necessary in the detergent used for foam washing.
Furthermore, when a detergent contains a silicate, the silicate easily deposits on a metal surface, becoming a core of stains, and is likely to stain easily the surface after washing.